The invention applies particularly to heat exchangers for exchanging heat between a first fluid flowing in a plurality of tubes forming a multi-tube bundle, and a second fluid flowing around the tubes in a cylindrical cavity defined by a hollow body (or shell) in which the bundle of tubes extends; the invention applies in particular to heat exchangers for engines, gear boxes, reversing means, compressors, hydraulic units, . . . In this type of heat exchanger, heat energy is transferred between the hot source and the cold sink in particular by conduction through the walls of the tubes. In order to obtain sufficient heat transfer flow (and/or heat exchange coefficient), the tubes are made of a material having high thermal conductivity, such as a metal alloy based on copper, aluminum, nickel, titanium, or stainless steels.
The invention applies in particular to such heat exchangers having two tube plates pierced by a plurality of orifices. Each one of the two ends of each tube is engaged in a corresponding orifice in one of the tube plates, and is secured to said plate in leaktight manner in particular by brazing, welding, or tube-expanding.
In addition to the tubes and the tube plates at its ends, the bundle of tubes may also include baffles for guiding the flow of the second fluid inside the hollow body. In general, such baffles are essentially constituted by thin plates extending transversely relative to the tubes and parallel to the end tube plates, they are regularly spaced apart along the tubes, and they serve to close off a fraction (generally a circular fraction) of the cross-section of the hollow body in order to guide the second fluid. The bundle may also have fins crimped or otherwise connected to the outside surfaces of the tubes of the bundles. It may also have other secondary surfaces.
As a general rule, such heat exchangers also include, at each of their two longitudinal ends, a cap (end tank) covering a respective one of said tube plates, and serving either to connect the heat exchanger to two ducts external to the heat exchanger for transporting the first fluid, or else for guiding said fluid if the cap is a “blind” cap, i.e. having no connection to an external duct.
The hollow body has an inlet orifice for admitting the second fluid into said cavity and also an outlet orifice for said fluid. The hollow body is generally constituted by a part of generally tubular shape provided at each of its two longitudinal ends with a respective annular flange. Each flange is pierced by a plurality of orifices extending along the longitudinal axis of the heat exchanger and receiving screws or similar fasteners enabling the body to be secured in leaktight manner to at least one of the tube plates and also to the two caps.
The bodies of small heat exchangers, and in particular heat exchangers having a maximum dimension of less than 0.25 meters (m)) are generally made by casting a metal alloy without applying pressure, the body and the flanges being cast as a single piece. That technique presents drawbacks: the inside face of the body needs to be machined over its entire length in order to present roughness and geometrical quality that are compatible with the use to which it is put; the outside faces of the flanges also need to be smoothed; such molded pieces frequently present defects in their material leading to porosity that is incompatible with their function as acting as a leakproof wall; worse, these defects can be inspected validly only after mechanical machining (boring, turning, . . . ); this leads to expensive pieces being rejected; the technique of casting without applying pressure (casting into sand molds) also makes it impossible to obtain walls that are thin.
French patent No. 623 803 proposes a multi-tube heat exchanger in which the body is constituted by a segment of ordinary pipe but does not have any end flanges. That technique makes it difficult and/or expensive to provide said cavity with leaktight inlet and outlet couplings for the second fluid.
Document EP-A-1 146 310 describes a heat exchanger whose extruded shell presents an external spline having the inlet and outlet orifices for the second fluid formed therein, thereby overcoming that problem. That heat exchanger does not have means for enabling the hollow body to be rigidly connected to the bundle of tubes, with mechanical connection between those two elements resulting essentially from contact (pressure) forces acting between said two pieces via sealing members such as O-rings, which sealing members are flattened (compressed) between pairs of cylindrical bearing faces respectively provided on each of two pieces. In the absence of the sealing members, the bundle would be free to slide inside the cavity of the body. In the presence of the sealing members, the bundle can still slide inside the cavity under drive from sufficient force, in particular under drive due to the tubes of the bundle lengthening because of thermal expansion. Each sealing member is received in an annular groove provided in the outside face of the corresponding tube plate. This makes it possible to avoid forming grooves in the inside face of the wall of the hollow body so that the wall then requires no more than a chamfer to be formed at the or each of its inside ends. That makes it possible to slide in a bundle whose tube plate is provided with the sealing gasket without damaging the gasket, and this also makes it easier to flatten the gasket.